What is a Sewer System Assessment? (SSA)
Collection system renewal is a continual process of finding system defects, prioritizing them and fixing them. The “find-it” portion of the program is commonly referred to as a sewer system assessment (SSA). The goal for the collection system manager may be to inspect the collection system on a 10-year cycle. (Note that critical sewers or those assets in flood prone areas may be on an annual cycle of inspection.) A ten year cycle will require inspecting/testing 10% of the collection system annually. The results of the inspection will generate repairs to manholes and mainline sewers. Private sector defects will also be identified requiring enforcement of local codes. Budgeting funds to find and fix system defects is the least cost solution to extend the life of the collection system another 75 to 100 years. Waiting for pipeline or manhole failure will require replacement of the assets which is the most expensive alternative (by several factors).
SSA may include these tasks:
- Flow monitoring – Temporary flow monitoring can be used to determine inflow/infiltration levels, prioritize areas for testing, calibrate dynamic hydraulic models, measure in-situ line capacity and detect bottlenecks within the system. The staff of Pipeline Analysis, LLC have experience with all the major equipment manufacturers. In addition, we have worked in pipelines from 6″ to 108″.
- Manhole/pipe inspections – During manhole inspection, field crews take a complete inventory of each manhole including construction materials, conditions, depth to invert, flow conditions, debris, along with infiltration/inflow and structural defects documentation. All inventory information is recorded in the project database and is used to develop maintenance and repair programs. Pipeline Analysis, LLC utilizes digital camera equipment during manhole inspection to document defects encountered.
- Smoke testing – Utilizing in-house designed high-capacity blowers, our staff has experience in locating and documenting rainfall induced infiltration/inflow. This relatively inexpensive defect location tool is very effective in identifying inflow sources and most restrictive conditions within the sewer lines on both public and private pipelines. Our documentation of defects using digital cameras, portable GPS and sketches ensures that proper repairs are recommended and defects can be relocated for repair. Notification of residents, fire and police departments is critical and our staff has the experience working with residents during testing and answering questions of concern.
- Dye flooding – Usually performed in conjunction with internal TV inspection, dye water flooding assists in the location and quantification of specific defects during an evaluation. The procedure consists of forcing non-toxic dye into defects located during smoke testing and manhole inspection. The path of the dye is then documented, and leaks in the sewer lines are located. Manholes with evidence of inflow/infiltration, mainline defects, cross-connections, roof drains and area drains can all be investigated using the dye flooding procedure.
- CCTV inspection – Internal TV inspection (using Pipeline Assessment Certification Program-PACP codes) is used to determine the exact nature of specific defects located during smoke testing and physical inspection. Using high definition miniature color cameras, the TV operator inspects the interior of sewer pipes looking for defects. Line segments are recommended for inspection when smoke testing indicates main line defects, chronic maintenance problems or observed hydraulic restrictions. Possible cross-connections with storm sewers are evaluated and least cost rehabilitation methods are determined by analysis of the CCTV results. Pipeline Analysis staff are PACP certified and we have a certified PACP trainer on staff.
- System Mapping – Accurate maps of the sanitary sewer system are critical to the success of maintenance or sewer system assessment programs. Map correction can provide updated information regarding line and manhole placement. The manhole numbering system is used in documentation of system defects in the project database. For digital mapping, Pipeline Analysis, LLC will utilize ArcView™ or CAD depending on the clients capabilities. The use of desk-top mapping allows Pipeline Analysis, LLC to display the data gathered from the field on the collection system map.
- Prioritized rehabilitation plan with estimated costs – A review of the field testing results and local conditions will result in preliminary rehabilitation recommendations. The final report prioritizes repairs so limited funds are budgeted and targeted where they will have optimum impact. Rehabilitation cost estimates will be based on local construction costs.
Rehabilitation methods available to extend the life of collection system assets (renewal of assets) include trenchless technologies that minimize the impact to customers. Manhole rehabilitation may include lining, sealing, installing water tight ring and covers, raising buried manholes to grade, replacing vented covers, etc. Mainline sewer rehabilitation may include cured-in-place pipe (CIPP), slip lining and upsizing or pipe replacement by pipe bursting. These “fix-it” technologies are expanding to service laterals which must be addressed by collection system managers.
For example, the capacity analysis performed in the master plan will impact sewer system renewal. Knowing when a particular pipeline will require upsizing will impact the decision to rehabilitate the pipe. It may be more cost effective to defer rehabilitation (yet maintain the pipe) and replace the pipe as part of the capital improvement plan (CIP). Also, the least cost renewal plan may require deferring some rehabilitation until sufficient quantities are identified to reduce unit repair costs. Utilization of term contracts for collection system renewal is gaining favor as it speeds up the process of rehabilitation and fixes unit prices, thus keeping projects within annual budgets.